Cryogenic systems are used throughout industry and research alike. Although the invention is not limited to such an application, of particular interest here is the application of cryogenic systems to space-related propulsion research. In this regard, most types of propulsion research rely heavily on the use of cryogenic fluids. Generally, these fluids include liquid oxygen (O2), liquid nitrogen (N2) and liquid hydrogen (H2). These cryogenic fluids are used for a variety of propulsion related requirements, such as cooling and combustion fuel/additives.
Cryogenic systems usually operate at high flow or nozzle pressures. For example, flow rates of up to 16 liters per second are common in pipes with 5 centimeter diameters. Fundamental data on physical attributes within the cryogenic liquid flow are difficult to measure. In this regard, even basic questions such as how much cryogenic liquid is actually traveling through the system are difficult to answer. At the operating temperatures of these cryogenic systems there is a constant mixing between the gaseous and liquid states. This can lead to turbulent flow and cavitation and make flow measurement difficult.
Current techniques for determining mass flow assume that there is no turbulence, which also precludes the presence of any gaseous medium in the flow. Due to the very nature of the low temperatures involved, the basic, conventional engineering measurement techniques normally used are either not available or inapplicable, or, if used, are error ridden. These conventional techniques include the use of direct contact thermocouple and thermoresistor measurements, as well as of flow-driven mechanical flow meters.